This invention relates generally to writing data to a disc drive including but not limited to a method and apparatus for initializing a memory in order to improve the writing of test data to an optical disc drive.
To write data to an optical compact disc (CD)such as a CD-Recordable (CD-R) or a CD-Rewritable (CD-RW) disc, a laser is selectively energized to create a pattern corresponding to the information to be recorded on the disc media. Not all recording mediums are alike, however, and laser power settings must be adjusted to compensate for the differences. In order to adjust the laser power, the laser is fired initially at a test area on the disc. The test area is referred to as the power calibration area (PCA). The optimum power setting for a particular optical recording medium can be influenced by a number of variables including the recording speed, humidity, ambient temperature and the type of disc being used. Thus, the amount of write power is determined each time a disc recording is made.
When determining the optimum write power, random, eight-fourteen modulation (EFM) data is recorded at different power levels to the PCA. The recorded data is read back and the asymmetry of the data written at each write power is measured. In general, an optimum power setting is achieved when both high and low frequencies share the same level of asymmetry.
Prior to recording, the EFM test data is stored in a buffer memory. The memory is first initialized with a zero bit sequence. After initialization, a pseudo-random data generator is enabled and generates random data which is stored in the memory. The write operation starts by encoding the data stored in the memory and writing that data to the disc while simultaneously generating and storing random data in the memory. Because the memory is initialized with a zero-bit sequence, the zero-bit sequence is encoded and stored on the disc. As a result, the data written for write power calibration is not all random data, and the presence of the zero-bit sequence statistically biases the write calibration results. This statistical bias results in calibration errors which, in turn, result in errors in writing data to the disc.
In view of the foregoing, a method and apparatus that initializes a memory with random data rather than zeros would be useful for providing unbiased random data for use in a write power calibration test. Such a method and apparatus would greatly improve the selection of the optimum write power in CD-R and CD-Rewritable (CD-RW) disc drives and thus provide increased reliability and performance.